Researchers at Harvard John A. Paulson School of Engineering and Applied Sciences have developed a compact photonic device capable of dynamically controlling the “handedness” of light, a property known as optical chirality. The system allows real time tuning of how light behaves as it passes through engineered nanostructures.
The work, led by Fan Du in the lab of Eric Mazur, introduces a reconfigurable photonic crystal platform integrated with micro electromechanical systems. By mechanically adjusting the structure, the device can modify how it interacts with polarized light, according to Harvard SEAS.
Photonic crystals are nanoscale materials designed to manipulate the propagation of light through periodic structures. In this system, two layers of silicon nitride photonic crystals are stacked and slightly rotated relative to each other, forming what is known as a twisted bilayer structure.
This approach is inspired by concepts from twistronics, where rotating layered materials creates new electronic or optical properties. When applied to photonics, the twist introduces asymmetry between left and right orientations, enabling control over circular polarization states of light.
Light can exhibit chirality by rotating in a helical pattern as it travels. These rotations are categorized as left circular or right circular polarization. While the difference is subtle, it plays a critical role in applications such as molecular analysis, optical communication, and quantum systems.
The Harvard device leverages this property by enabling selective interaction with one polarization state over the other. When light enters the structure, the twisted geometry causes different transmission responses depending on its handedness.
A key innovation is the integration of a micro electromechanical system, which allows precise control over both the rotation angle and the spacing between the two layers. This enables continuous tuning of the device’s optical response without requiring physical replacement of components.
Traditional optical components used to analyze or manipulate polarization, such as wave plates and polarizers, are typically static and limited in range. In contrast, this system provides a tunable platform capable of adapting to different wavelengths and polarization states in real time.
The researchers demonstrated that the device can achieve near perfect selectivity when distinguishing between left and right circularly polarized light under normal incidence conditions. This level of control is achieved through strong coupling effects between the two photonic layers.
From an engineering standpoint, the system is compatible with existing photonic fabrication processes, making it suitable for integration into chip scale devices. This opens the possibility of embedding advanced light control directly into optical circuits.
Potential applications include chiral sensing, where detecting molecular differences is critical in fields such as pharmaceuticals and chemistry. The technology could also be used in optical communication systems, where dynamic control of light properties enables higher data density and improved signal processing.
In quantum photonics, precise manipulation of light states is essential for encoding and transmitting information. A tunable platform such as this could support more flexible and scalable quantum systems.
The device remains a proof of concept, but it demonstrates how combining nanophotonic structures with mechanical control systems can expand the functional range of optical components.
